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For a low-carbon steel part that will be put into a long lifetime use (10 years plus) what are recommended load cases to consider creep? The part I'm specifically working with will have a relatively low cycle count (20k load cycles over ten years) at about 10% of it's yield strength Loads are compression and tension loads with no load being it's 'normal' position.

Is there a percentage of yield strength that calculating creep worth considering? Are there material properties that are more critical? Is cycle count more critical?

And, how do you go about calculating creep? I vaguely remember doing this in university but can't find any simple questions.

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  • $\begingroup$ what temperature? $\endgroup$ – agentp Dec 1 '17 at 19:29
  • $\begingroup$ Can be assumed to be constant temp at 24 degrees C $\endgroup$ – Diesel Dec 1 '17 at 19:57
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    $\begingroup$ forget about it, you won't even find data for creep of steel below maybe 500c. $\endgroup$ – agentp Dec 1 '17 at 20:03
  • $\begingroup$ So creep below 500C never occurs at all? $\endgroup$ – Diesel Dec 1 '17 at 20:08
  • $\begingroup$ not at room temp at 10% of yield. If steel crept there all our bridges would be sagging. If you are concerned about incredibly small strains for some reason that also may be another matter. $\endgroup$ – agentp Dec 1 '17 at 20:17
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creep is caused when applied stresses in a metal part can be relieved by movement of metal atoms via diffusion within the crystal lattice. diffusive transport only becomes important when the service temperature exceeds about 1/3 to 1/2 the melt temperature (rough rule of thumb, using degrees K)- meaning steel doesn't creep at room temperature but lead/tin solder does. the materials science text by Van Vlack covers this topic in more detail.

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